Is there a "Null" or a "None" for Graphics?
If I want to accomplish something like
g1 = Graphics[---];
g2 = Graphics[---]
g3 = If[test, Graphics[---], NoGraphics ];
Show[g1, g2, g3 ];
is there something I can put in for "NoGraphics" (other than an
offscreen Point or a zero-size Point or . . . ) that will be acceptable
in subsequent graphics commands